The field of the invention is systems and methods for magnetic resonance imaging (“MRI”). More particularly, the invention relates to systems and methods for gradient-modulated sweep imaging with Fourier transformation (“GM-SWIFT”) MRI.
In conventional MRI sequences, the time elapsing between spin excitation and signal acquisition, which is known as the echo time (“TE”), is typically too long to detect nuclei with short transverse relaxation times (“T2”) or effective transverse relaxation times (“T2*”). This is problematic for imaging highly ordered tissues (e.g., tendons and knee meniscus) and highly mineralized tissues (e.g., bone, teeth).
Short T2* sensitive sequences like ultra-short echo time (“UTE”), back-projection low angle shot (“BLAST”), and rotating ultra-fast imaging sequence (“RUFIS”) have been developed to detect signals from ultra-short T2* spins. In addition to these sequences, a new type of pulse sequence called sweep imaging with Fourier transformation (“SWIFT”) was introduced.
SWIFT uses swept radio frequency (“RF”) excitation and virtually simultaneous signal acquisition in a time-shared mode. It provides the ability to capture signal with ultra-short T2* in the microsecond range, and has already found several applications. On the other hand, the deposition of specific absorption rate (“SAR”) becomes a serious concern with increasing field strength, especially during imaging of fast relaxing spins, which usually require a high excitation bandwidth (“BW”). This creates even more problems for experiments using big volume and potentially power-inefficient RF coils.
There remains a need for a method for magnetic resonance imaging that provides the ability to acquire ultra-short T2* signals while reducing SAR, especially at higher field strengths.